Interactions of Dietary Antioxidants and Methylmercury on Health Outcomes and Toxicodynamics: Evidence from Developmental Rat Model Studies and Human Epidemiology

Abstract

The contamination of seafood with methylmercury (MeHg) is a global health issue, as MeHg is a well known neurotoxin. Since dietary nutrients may interact with MeHg toxicity, and oxidative stress is one of the primary mechanisms underlying MeHg neurotoxicity, we characterized dietary antioxidant-MeHg interactions. Firstly, we used an ethnobotanical study to confirm the antioxidant activity of Northern Labrador Tea, Rhododendron tomentosum ssp. subarcticum (Tea), for the Canadian Inuit, a population with elevated MeHg exposure. Secondly, we determined the ability of Tea to ameliorate MeHg-induced toxicity in a rat perinatal exposure study. MeHg exposure (2 mg/KgBW/d) was associated with perturbed development and behaviour, elevated brain N-methyl-D-aspartate receptors, and serum lipid peroxidation. Surprisingly, Tea co-exposure (100 mg/KgBW/d) modulated MeHg’s effects on brain NMDA-R levels and lipid peroxidation, but also increased mercury serum concentrations. Thirdly, using a toxicogenomics approach we determined that MeHg exposure caused the down-regulation of Nr4a2 and its protein product Nurr1. These novel MeHg targets are implicated in developmental learning functions and were corrected with MeHg + Tea co-exposure. Lastly, we conducted a risk assessment survey and cross-sectional dietary epidemiology study in Costa Rica to further investigate dietary nutrient-MeHg interactions. Costa Rica is a Central American country with multiple sources of Hg and a high per capital fish consumption. Here, 5 of the 14 populations we studied exceeded the recommended MeHg provisional tolerable daily intake (pTDI) of 0.2 µg/KgBW/d. In Heredia the pTDI was exceeded by 34% of woman participants, primarily associated with canned tuna consumption. Interestingly, we detected that Hg body burden was significantly reduced by the consumption of antioxidant-rich dietary items. Considering our collective results, we hypothesized that MeHg toxicokinetics may be altered by dietary nutrients at the site of intestinal absorption from the disruption of gut flora, or at the site of cellular demethylation in tissues from the improvement of cellular redox state. The interaction of dietary nutrients on MeHg outcomes has a large impact on risk assessment and may provide a public health approach for managing the risk associated with MeHg exposure without reducing local fish consumption.